Question regarding the GRU

I'm writing a fictional story taking place in 1933 Leningrad. I'm thinking of involving the GRU in the plot but I'm unsure about some questions regarding authority and secrecy.

How secret was GRU in 1932? How will an agent of the GRU present himself to a low level party representative or militia officer if he wants to question them regarding a foreign diplomat?

What kind of authority did the GRU have on Soviet territory 1933? Could they arrest people or do they need to use the militia or the OGPU in order to detain someone? How strong was the rivalry with the OGPU during this time? What kind of reactions is probable if the local chekists feels that the GRU is standing on their turf?

To my knowledge, GRU was not generally spoken of, so an agent would have some sort of cover. Presumably, he'd also be a party member, so access to different things shouldn't be too difficult.

If you are writing a novel, a lot of "need to know" would likely take place. In the early thirties, fascist spies, saboteurs, anti-soviet elements and general paranoia are everywhere, so it'd be a volatile period. The civil war is still in living memory after all.

I am honestly not sure what authority they would have, but soviet intel organizations generally had pretty far reaching authority. Of course, bureacracy will rear it's ugly head, and in many cases, it may come down to who has the most high-ranked connection, rather than formal authority.

GRU was pretty independent minded, though it was also infiltrated by the Cheka (according to wiki). It's primary purpose would be military intel of course

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